There is no formal KDE company - there is the not for profit KDE e.V, but it does not direct development in any way.

However, if you are interested in a light weight window manager or desktop environment, I would suggest a look at environments such as Xfce, or attempting to customise KWin / Plasma to suit your needs. Both are fairly configurable.

It may be easier to help point you in the right direction however if more information was available. What are you attempting to achieve exactly with a "light weight" WM / DE?